Method and device for the production of tubular members of silicon

ABSTRACT

A method and device for the production of silicon tubes by deposition of self-supporting silicon layers from the gas-phase onto tubular heated carriers of graphite whereby two such vertical carriers are supported along the periphery of their lower ends by electrodes and are connected at their upper ends by a bridge of conductive material, whereby the tubular shaped carriers, as well as the supporting electrodes and the connecting bridge are so designed with respect to each other that the respective values for the product of the shortest circumference with the smallest current carrying cross-section and the specific conductivity for the electrodes and connecting bridge are at least five times, preferably ten times as large as the values of such products for the tubular carriers, and stopping the production of such layers when the temperature differential between the tubular carriers and the supporting elements, i.e., electrodes and connecting bridge, drops to 300*C.

Dietze METHOD AND DEVICE FOR THE PRODUCTION OF TUBULAR MEMBERS OF SILICON Inventor: Wolfgang Dietze, Munich, Germany Siemens Aktiengesellschaft, Berlin and Munich, Germany Filed: Sept. 25, 1972 Appl. No.: 291,787

Assignee:

Foreign Application Priority Data Oct. 4, 1971 Germany 2149526 US. Cl 425/447, ll8/49.l, 425/470 Int. Cl. B29c 13/00, C23c 13/08 Field of Search ll8l4849.5;

[ June 28, 1974 Primary Examiner-Morris1(aplan Attorney, Agent, or FirmHill, Gross, Simpson, Van Santen, Chiara & Simpson [5 7] ABSTRACT A method and device for the production of silicon tubes by deposition of self-supporting silicon layers from the gas-phase onto tubular heated carriers of graphite whereby two such vertical carriers are supported along the periphery of their lower ends by electrodes and are connected at their upper ends by a bridge of conductive material, whereby the tubular shaped carriers, as well as the supporting electrodes and the connecting bridge are so designed with respect to each other that the respective values for the 7 product of the shortest circumference with the smallest current carrying cross-section and the specific conductivity for the electrodes and connecting bridge are at least five times, preferably ten times as large as the values of such products for the tubular carriers, and stopping the production of such layers when the temi perature differential between the tubular carriers and the supporting elements, i.e., electrodes and connecting bridge, drops to 300C.

QIELLSLIDRTELWEEESEED METHOD AND DEVICEFOR THE PRODUCTION OF TUBULAR MEMBERS OF SILICON BACKGROUND OF THE INVENTION The invention is directed to a method and device for the production of tubular members of silicon by the de-' position of self-supporting silicon layers from the gasphase upon tubular heated carriers formed, for example, of graphite, from which the silicon layers comprising the desired tubes may be removed. Such device may comprise a pair of parallel carriers, supported in vertical positions by respective electrodes which contact the carriers along the peripheries thereof at their lower ends, with the upper ends of the carriers being connected by a bridge member of conductive material. The reaction container is provided with means for supplying a flowing reaction gas comprising a halogenized silane and hydrogen, as well as an outlet for the exhaust gases, with the two electrodes supporting the respective carriers being adapted to be conductively connected to opposite sides of a suitable current source, which may be either a direct current source or a low frequency alternating current source.

U.S. Pat. application No. 1 13,286, now U.S. Pat. No. 3,746,496, generally illustrates a device of this type and the present application is directed to an improvement of such type of device.

Operation of structures of this type, however, has revealed the disadvantage that the deposited layer was not limited to the surface of the carriers, as desired, but readily extended over other parts of the apparatus, particularly the connecting bridge and the electrodes. Upon withdrawal of the tube-shaped carriers from the electrodes and from the connecting bridge, damage of the Si layer on the surface of the tubular carriers readily occurred, whereby the layer no longer could be easily removed therefrom. The present invention therefore is directed to the problem of so constructing and oper ating a device of this type that the above-referred to disadvantage is automatically eliminated.

SUMMARY OF THE INVENTION In order to achieve the desired results, in accordance with the present invention, the tubular carriers, as well as the supporting electrodes and connecting bridge therefore, are so designed that the product of the shortest circumference with the smallest current-conducting cross section and the specific conductivity of the material of the electrodes and connecting bridge are at least five times, preferably at least ten times greater than that of the tubular carriers.

Preferably, such components consist of highly pure conductive carbon, particularly graphite, and in this event, the operational current should be initiated only if the reaction chamber is filled with an inert gas or hydrogen to prevent burning of such components.

If an alternating current source is employed, it should have a sufficiently low frequency that the supplied current has no noticeable skin-effect with respect to the tubular carriers or the electrodes and the connecting bridge. This is generally the case when alternating current from an interconnection is involved.

Upon passage of the operational current, the temperature at the surface of the tubular carriers automatically increases by at least 300C over the surface temperatures of the electrodes and the connecting bridge. Consequently, if a mixture of halogenized silane (especially FiCl FiHClor the corresponding bromine compounds) and hydrogen are employed as the reaction gas, the temperature at the surface of the tubular carriers should be adjusted to not more than l,250C whereby the temperature at the connecting bridge and at the electrodes will be so low that a deposition at the surface of these components cannot occur.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, wherein like reference parts indicate like or corresponding parts, the FIGURE illustrates a vertical section through a device constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawing, the reference numeral 1 designates a base member or plate, of quartz or other heat-resistant metal or material, which is hermetically connected with a dome-shaped member 2, in effect forming a bell jar which may, for example, be constructed of quartz. Disposed in the chamber thus formed are two vertically extending tubular carriers 3 which have their lower end inserted into respective bores 4, formed in supporting electrodes 5, with the electrodes being conductively connected with feed lines 1 1, extending through the base plate 1 in insulated relation with respect thereto and thus with respect to each other.

The tubular carriers 3 are connected at their upper ends by a conductive bridge member 6, preferably constructed of the same material as the carriers 3, with the upper ends of the latter being disposed in respective bores 7 formed in the bridge 6. The bores 4 and 7 are each slightly tapered inwardly whereby the side walls of the bores 4 taper downwardly when thoseof the bores 7 taper upwardly. As a result of the geometric configuration, the respective ends of the carriers 3 fit very snugly into the electrodes and bridging member to provide a substantially perfect electrical contact. The interior of the tubes 3 may, by means of the bores 7, be open to the reaction chamber, and by disposing the open end of each respective supply line 8 adjacent the outer ends of the respective bores 4 in the electrodes 5, the gas entering the device may flow through the in terior of the carriers 3, to provide a cooling action on the interior surfaces of the latter. The cooling gas may, in this case, be one participating directly in the reducing reaction, or in the form of an inert gas, for example, argon or nitrogen which thus may also function as a diluting medium for the active component of the reaction gas.

The reaction gas may consist, for example, of a halogenized in particular chlorinated, silane (for example SiHCl or SiCl and hydrogen. Such gas may enter through a feed line 9 located in the bottom 1 of the reaction chamber, and in the example illustrated, an exhaust tube 10 for the exhausted gas is disposed concen trically to the supply tube 9, the latter however, extending a greater distance into the chamber than the exhaust outlet 10, with both being located between the two tubular carriers 3.

By utilizing carrier temperatures which do not exceed a value of l,250C and by effective cooling of other areas, it can be assured that the deposited layers can be completely and efficiently removed from the carriers.

As previously mentioned, in accordance with the present invention, the tubular carrier as well as the carrier-supporting electrodes and the connecting bridge are so designed with respect to one another, that the value of the product of the shortest circumference with the smallest current-conducting cross section and the specific conductivity of the electrodes and the connecting bridge are at least 5 times, preferably ten times as large as the value of the corresponding product for the tubular carriers.

Likewise, preferably, such parts are constructed of highly pure conductive carbon, particularly graphite, in which case the operational current should be initiated only if the reaction chamber is filled with an inert gas or hydrogen to prevent the burning of such components.

As also previously mentioned, if an alternating current source is employed it should have a sufficiently low frequency that the supplied alternating current has no noticeable skin-effect in the tubular carriers, electrodes or connecting bridge.

If a mixture of halogenized silane (especially SiCl or SiHCl or corresponding bromine compounds) and hydrogen are employed as the reaction gas, the temperature at the tubular carriers is adjusted to not more than 1,250C so that at all times the temperature at the connecting bridge and at the electrodes is so low that a de position on the surface of such components cannot occur.

Normally the tubular carriers will be cylindrical or prismatic in which case the circumference of each horizontal cross-section equals the shortest circumference whose value is to be included in the above defined product. This likewise applies to the electrodes 5. The shortest circumference of the connecting bridge, however, will be determined by a comparison of the circumference or peripheries of the cross-sections which extend vertically to the connecting line of the upper ends of the two tubular carriers. In most cases the smallest circumference simultaneously constitutes the circumference of the smallest current-carrying crosssection. The cross-sectional area of the smallest current-carrying cross-section, as well as the tubular carriers, electrodes and connecting bridge are also incorporated in the above mentioned product. In the event that all of these components are constructed from the same material, differences in conductivity of the various arts do not have to be taken into consideration.

It is particularly advantageous if the connecting bridge and the electrodes have more or less stud-like projections at the connecting points for the tubular carriers, which after assembly of the latter extend somewhat into the interior of the tubular carriers and thus come in contact with the inner walls thereof. This construction results in a lesser heating of the ends of the tubular carriers, and deposition of silicon is thus avoided at these points. This likewise results in an improvement in separating the tubular layers from the carriers following the depositions.

As will be obvious from a reference to the drawing, the present invention may be readily incorporated in the construction illustrated in the previously referred to patent application. The wall thickness of the tubular carriers 3 is, for example 3 mm while the minimum wall thickness of the electrodes 5, as well as that of the connecting bridge 6 are 20 mm,- so that upon adjustment of the temperature at the surface of the tubular carriers to l,200C, the temperature at the surfaces of the connecting bridge and the electrodes will not exceed 800C, whereby deposition will not take place thereon.

In the arrangement illustrated, the bridge 6 is in the form of a relatively massive member in which the crosssection thereof may be considered the wall thickness. However, advantageously, such current-conductive connecting bridge is provided with a hollow interior forming a connecting chamber for inert gas whereby the same may flow from one carrier, through the chamber into the other carrier, thus further reducing the temperature of the bridge.

It is also possible to use the same reaction gas as the cooling gas at the inlet lines 8 so that such gas enters the chamber through both the inlet lines 8 and the line 9. In this case, a deposition will occur on the internal face of the tubular carrier as well as on the exterior face thereof, whereas the connecting bridge 6 and the electrodes otherwise remain sufficiently cool to avoid a deposition thereon.

It will be appreciated that in operation, a limitation of the thickness of the deposited layers should also be taken in consideration. As the growing layer increases in thickness, the temperature will constantly be increasing at the electrodes 5 as well as at the connecting bridge 6, in comparison to the temperature at the surface of the already deposited Si layer. It therefore is ad vantageous to terminate the deposition if the temperature difference between the depositing area at the already deposited layers 12, and the bridge 6 or the electrodes 5, respectively has decreased to a value of 300C. It therefore is recommended that such differential be monitored during the deposition process, which can, for example, be effected by means of thermoelectrical probes or optical pyrometers.

The deposited silicon layers can be readily separated from the tubular carriers irrespective of whether the deposition was effected on the external or internal walls of the carrier.

Having thus described my invention it will be obvious although various minor modifications might be suggested by those versed in the art, it should be understood that I wish to employ within the scope of the patent granted hereon all such modifications as reasonably, and properly come within the scope of my contribution to the art.

What I claim is:

1. A device for the production of tubular members of silicon by deposition of self-supporting silicon layers from the gas phase upon heated tubular carriers from which the silicon layers forming the desired tubes are removed, comprising a reaction vessel in which are disposed a pair of parallel tubular carriers supported in vertical position by electrodes which contact the carriers along their periphery at their lower ends, a bridge of conductive material connecting said carriers at their upper ends, means in the reaction container for supplying thereto a reaction gas flow comprising halogenized silane and hydrogen, and means forming a discharge for exhausted gas, the two electrodes supporting the carriers being adapted to be conductively connected to opposite sides of a current supply source, the values of the products of the shortest circumference with the smallest current conducting cross-section and the specific conductivity of the connecting electrodes and connecting bridge respectively being at least five times,

preferably at least times, that of the value of such product for the respective tubular carriers.

2. A device according to claim 1, wherein the tubular carriers, connecting bridge and electrodes supporting the carriers are constructed of conductive carbon.

3. A device according to claim 2, wherein the tubular carriers connecting bridge and electrodes are constructed of highly pure graphite.

4. A device according to claim 1, comprising in fursame. 

1. A device for the production of tubular members of silicon by deposition of self-supporting silicon layers from the gas phase upon heated tubular carriers from which the silicon layers forming the desired tubes are removed, comprising a reaction vessel in which are disposed a pair of parallel tubular carriers supported in vertical position by electrodes which contact the carriers along their periphery at their lower ends, a bridge of conductive material connecting said carriers at their upper ends, means in the reaction container for supplying thereto a reaction gas flow comprising halogenized silane and hydrogen, and means forming a discharge for exhausted gas, the two electrodes supporting the carriers being adapted to be conductively connected to opposite sides of a current supply source, the values of the products of the shortest circumference with the smallest current conducting cross-section and the specific conductivity of the connecting electrodes and connecting bridge respectively being at least five times, preferably at least 10 times, that of the value of such product for the respective tubular carriers.
 2. A device according to claim 1, wherein the tubular carriers, connecting bridge and electrodes supporting the carriers are constructed of conductive carbon.
 3. A device according to claim 2, wherein the tubular carriers connecting bridge and electrodes are constructed of highly pure graphite.
 4. A device according to claim 1, comprising in further combination, means for supplying an inert cooling gas to the interior of the tubular carriers.
 5. A device according to claim 1, comprising in further combination, means for supplying a quantity of the same reaction gas, utilized for the deposition operation, to the interior of the tubular carriers for cooling the same. 